Cardiovascular Responses to Commonly Used Tests In and Outside of the Laboratory Settings

Several tests are available for assessing cardiovascular response to various interventions which may be given in the laboratory, or outside of it in the field. The tests are meant to excite or deactivate cardiovascular and other sensory receptors which signal the central mechanisms. They have been found useful in generating data to study cardiovascular effects on subjects exposed to specialized physical training (e.g., athletes), in the evaluation of people engaged in special occupations such as pilots, astronauts, and other military personnel, and in training undergraduate and postgraduate students. If the response does not fit into the physiological norm, it may reflect a temporary aberration, or a more serious defect in the cardiovascular control mechanism because of disease. Interpretation of data generated may vary between various operators/observers. Here, an attempt has been made to bring out responses of the cardiovascular system to the commonly used tests, and their applicability in clinical situations.

Current Concepts of Pathophysiology of Vasovagal Syncope and its Evaluation and Management: A Review

Vasovagal syncope (VVS) with a sudden, temporary loss of consciousness (LoC) is a common phenomenon in the young and the elderly. Though generally described as innocuous, it may lead to serious consequences in special category of people (pilots), or in the elderly in whom LoC may lead to a fall and serious injury. The topic has been copiously researched upon and discussed in medical literature over the last few decades, but the exact mechanisms which lead to the disability have yet to be fully agreed upon. Changes in cardiovascular baroreceptor sensitivity, aberrations in the complex interaction amongst the nucleus of the tractus solitarius and the nuclei around it, inability of the peripheral circulation to respond to autonomic vasoconstrictors, or excess production of vasodilators such as nitric oxide produced locally have been considered in its pathophysiology. Various extraneous situations like dehydration, exposure to heat stress, medications, psychological factors may adversely stress regulatory physiological responses and promote occasional episodes of VVS. More complex dysautonomia could be a reason for the recurrent VVS. Differences between brain structure of VVS sufferers and normal subjects have been proposed. Head-up tilt table (HUT) test is the most widely applied investigation for evaluating VVS episodes. Lower body negative pressure (LBNP) has also been used. Enhancement of the orthostatic stress may be done by simultaneous use of both, or with peripheral vasodilators. As to whether such an enhancement is necessary is debatable. Management with increased salt and fluid intake, corticosteroids, beta adrenergic receptor blockers, alpha adrenergic receptor stimulants, selective serotonin reuptake inhibitors, and nitric oxide synthase inhibitors have been tried with variable success.